Actuators for stroke control in hydraulic machines

ABSTRACT

An actuator for varying the stroke of a variable stroke swash plate pump in which there is provided a body defining a cylinder within which slides a differential area, hollow piston connected to the swash plate of the pump. A passage connects the cylinder in the smaller area side of the piston with whichever of the ports of the pump is at the higher pressure via a shuttle valve. A spool valve is slidable in a sleeve in the hollow piston and has a sleeve secured thereto. The hollow in the piston is connected on one side of the spool valve with a chamber in the pump and on the other side of the spool valve with the cylinder on the larger area side of the piston. A plunger is connected with the spool valve via the sleeve secured thereto and carries an abutment against which an element slidable in a further chamber is urged by a spring. The further chamber is supplied with a control pressure signal which controls the movement of the spool valve so that the magnitude of a servo pressure derived from the pump port pressure is controlled, with the servo pressure being applied to the larger area side of the piston via the spool valve.

United States Patent Jones Sept. 10, 1974 ACTUATORS FOR STROKE CONTROL IN HYDRAULIC MACHINES [57] ABSTRACT lnvemofl Brian Paul Jones, Huyton, England An actuator for varying the stroke of a variable stroke swash plate pump in which there is provided a body [73] Asslgnee' Jqsep-h Lucas (Indusmes) Lumted defining a cylinder within which slides a differential Birmingham, England area, hollow p1ston connected to the swash plate of Filedl 1973 the pump. A passage connects the cylinder in the [21] APPL No; 332,206 smaller area side of the piston with whichever of the ports of the pump is at the higher pressure via a shuttle valve. A spool valve is slidable in a sleeve in the US. Cl. hollow piston and has a leeve secured thereto The [51] Int. Cl. hollow in the piston is connected on one ide of the Field of Search 213, spool valve with a chamber in the pump and on the 60/452 other side ofthe spool valve with the cylinder on the larger area side of the piston. A plunger is connected References Cited with the spool valve via the sleeve secured thereto and UNlTED STATES PATENTS carries an abutment against which an element slidable 2,284,897 6/1942 Harrington 417/213 in a further Chamber is urged y a P The further 3,017,750 l/l962 Kempson 417/218 Chamber is pp with a Control Pressure Signal 3,667,867 6/1972 Boydell etal 417/222 which controls the movement of the spool valve so 3,669,570 6/1972 Himmler 417/222 that the magnitude of a servo pressure derived from 3,736,073 5/1973 Walmsley 91/505 the pump port pressure is controlled, with the ervo pressure being applied to the larger area side of the Primary Examiner-William Freeh piston via the pool va]ve Assistant Examiner-G. P. LaPointe Attorney, Agent, or Firm--l-lolman & Stern 9 Chums 5 Drawing Figures PATENIED SEP 1 01914 sum 1 or '2 mm 1%58 fi mm 2 ACTUATORS FOR STROKE CONTROL IN HYDRAULIC MACHINES BACKGROUND OF THE INVENTION This invention relates to actuators for varying the strokes of rotary hydraulic machines.

SUMMARY OF THE INVENTION According to the invention, an actuator arrangement for varying the position of a stroke control on a variable stroke rotary hydraulic machine comprises a piston engageable with said stroke control, means for subjecting one side of said piston to a first pressure signal, a valve spool slidable within said piston to control the magnitude of a servo pressure derived from said first pressure signal, said servo pressure being applied to the other side of said piston, with variations in said servo pressure arising from relative displacement between said piston and said spool urging said piston in directions to reduce said relative displacement, a chamber axially aligned with said piston, a plunger slidable within said chamber, and coupled to said spool, means for supplying a second pressure signal to said chamber, an element slidable within said chamber and engageable with an abutment on said plunger, and means biasing said element against said abutment to urge the plunger against said pressure signal.

Examples of the invention will now be described with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows, somewhat diagrammatically, an arrangement for varying the stroke of a hydraulic pump,

FIG. 2 is a detail of an alternative form of arrangement, and

FIGS. 3, 4 and 5 show diagrams of hydraulic circuits with which the invention is used.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1 a hydraulic pump has a plurality of axial pistons which engage, via slippers 11, a swash plate 12. The swash plate 12 is mounted on a trunnion (not shown) about the axis of which it is movable by means of an arm 13 carried by a piston 14 slidable in a cylinder 15. The pump includes a pair of ports (not shown) and a shuttle valve 16 having passages 17,18 respectively connected to a corresponding one of the ports. The valve 16 also has a passage 19 connected to an end of the cylinder so that the cylinder 15 communicates with whichever of the pump ports is at the higher pressure to urge the piston 14 leftwards as seen in FIG. 1. The effective area of the side of piston 14 adjacent passage 19 is, as shown, less than the effective area of the other side.

The piston 14 has an axial bore 32 which opens into a chamber 33 within the pump. The piston 14 includes a sleeve 26 within the bore 32, the sleeve 26 having ports 27 which communicate, through the wall of the piston 14, with the cylinder 15. The sleeve 26 also has an annular recess 28. A spool valve is slidable within the sleeve 26.

A sleeve 34 is secured to the valve 20 and is engageable with opposite ends of a chamber 35 within the piston 14 to limit axial movement of the valve 20 relative to the piston 14. Passages 38 allow the chamber 35 to communicate with an end of the cylinder l5 remote from the passage 19. The valve 20 has, moreover, an axial chamber 29 from which a pair of transverse passages 30,3l open to the outside of the valve 20. The arrangement is such that the passage 30 can communicate simultaneously with the port 27 and the chamber 35, and in this condition the recess 28 in the sleeve 26 is isolated from the bore 32 but communicates with the passage 31. The arrangement is also such that when the valve 20 has moved sufficiently far to allow the recess 28 to communicate with the bore 32, the passage 30 communicates only with the chamber 35.

Secured to the valve 20 by sleeve 34 is a plunger 36 which extends into a cylindrical chamber 37 axially aligned with piston 14. Secured to the plunger 36 is a threaded extension piece 38. Extension piece 38 has an axial through-bore 39 and transverse bores 40, whereby the end of plunger 36 is subjected at all times to the pressure within chamber 37. A pair of locked-up nuts 41 on the extension piece 38 provide an abutment against which a piston-like element 42 is biased by a spring 43 which lies within chamber 37. Extension piece 38 passes axially through element 42 with substantial clearance. The extension piece 38 is urged by spring 43 into abutment with a threaded adjustable stop 44 in an end wall 45 of chamber 37.

Passages 46, 47 and 48 communicate with chamber 37. In the arrangement shown passage 47 is closed off by a blanking plug 49 and passage 48 communicates via a flow restrictor 50 with a low pressure drain connection 51.

In use, the pump forms part of a hydraulic circuit, as shown in FIG. 3, with which includes a hydraulic motor and a booster pump 56, the actuator arrangement previously described being shown generally at 52. A control pressure Fe is applied to chamber 37 via passage 46. A pressure signal obtained from the high pressure port of the pump is supplied via valve 16 to the cylinder 15 to urge the swash plate 12 towards a maximum-stroke position. When passage 30 is in communication with both port 27 and chamber 35, the piston 14 is moved to the right until recess 28 communicates with bore 32 and the resultant pressure drop in chamber 35 causes piston 14 to move, relative to the valve 20, to the position shown in the drawing, at which relative position it is in equilibrium. The piston 14 will follow any subsequent movement of the valve 20. Movement of the valve 20 to the right or left respectively causes piston 14 respectively to increase or decrease the stroke of the pump.

As shown in FIG. 1, when extension 38 abuts stop 44 the resultant position of piston 14 is such that swash plate 12 is in a position corresponding to zero stroke of the pump. An increase in control pressure Pc urges plunger 36 to the right as seen in FIG. 1, and piston 14 I follows plunger 36 to increase the stroke of the pump.

The detail shown in FIG. 2 forms part of an arrangement substantially as above described, but including an extension piece 60, corresponding to extension 38 but of shorter length. Extension 60 is connected to plunger 36 and passes with clearance through member 42, as before. The arrangement of FIG. 2 forms part of a variable stroke hydraulic motor 61 (FIG. 4). Motor 61 itself forms part of a hydraulic circuit powered by a pump 62 and supplied by a boost pump 63.

The effect of the shortened extension 60 is that the swash plate of motor 61 is in a position corresponding to maximum stroke when extension 60 abuts the stop 44. An increase in control pressure Pc thus causes piston 14 to decrease the stroke of motor 61.

An actuator arrangement as shown and described with reference to FIG. 1 may also be used to maintain the power output of an associated motor substantially constant. For this purpose, pressure Pc is obtained from the pressure at the outlet of a motor 64, as shown in FIG. 5, the pressure in passage 19 being, as before, substantially that in the high pressure port of an associated pump 65. The diameter of plunger 36 and the rate of spring 43 are such that the product of pressure Po and the motor stroke remains substantially constant.

The alternative form of actuator described with reference to FIG. 2 may be used to maintain the output pressure of an associated pump substantially constant. In this case pressure Pc is obtained from the pump output pressure, increase in Pc tending to reduce the stroke of the pump.

I claim:

1. An actuator arrangement for varying the position of a stroke control on a variable stroke rotary hydraulic machine, said arrangement comprising a piston engageable with the stroke control, means for subjecting one side of said piston to a first pressure signal, a valve spool slidable within said piston to control the magnitude of a servo pressure derived from said first pressure signal, said servo pressure being applied to the other side of said piston, variations in said servo pressure arising from relative displacement between said piston and said spool urging said piston in directions to reduce the relative displacement, a chamber axially aligned with said piston, a plunger slidable within said chamber and coupled to said spool, means for supplying a second pressure signal to said chamber, and element slidable within said chamber and engageable with an abutment on said plunger, means biasing said element against said abutment to urge said plunger against said second pressure signal, and an extension of said plunger, in the region of said chamber, having bores therein which are in constant communication with said chamber so as to be subjected at all times to pressure within said chamber.

2. The arrangement according to claim 1, wherein said chamber is connected to a low pressure drain via a restrictor 3. The arrangement according to claim 1, wherein said plunger is provided with a nut assembly thereon forming said abutment, said element is mounted with a clearance on said plunger, and said biasing means comprises a spring mounted in said chamber and disposed to urge said element into engagement with said nut assembly.

4. The arrangement according to claim 1, wherein an adjustable stop is provided for limiting axial movement of said plunger by said biasing means.

5. The arrangement according to claim 4, such that abutment of said plunger against said stop, in use, corresponds to a position in which the machine is at zero stroke.

6. The arrangement according to claim 5, such that abutment of said plunger against said stop, in use, corresponds to a position in which the machine is at the maximum stroke.

7. A hydraulic pump and motor system incorporating an actuator arrangement as claimed in claim 1, wherein the actuator arrangement is connected with a stroke control for the pump, the first pressure signal is derived from that side of the pump which, in use, is at a higher pressure and the second pressure signal is derived from a control pressure.

8. A hydraulic pump and motor system incorporating an actuator arrangement as claimed in claim 1, wherein the actuator arrangement is connected to a stroke control for the motor, the first pressure signal being derived from that side of the motor which, in use, is at a higher pressure and the second pressure signal is derived from a control pressure.

9. A hydraulic pump and motor system incorporating an actuator arrangement as claimed in claim 1, wherein the arrangement is connected to a stroke control for the motor, the first pressure signal is derived from that side of the pump which, in use, is at a higher pressure and the second pressure signal being derived from the pressure at an outlet of the motor. 

1. An actuator arrangement for varying the position of a stroke control on a variable stroke rotary hydraulic machine, said arrangement comprising a piston engageable with the stroke control, means for subjecting one side of said piston to a first pressure signal, a valve spool slidable within said piston to control the magnitude of a servo pressure derived from said first pressure signal, said servo pressure being applied to the other side of said piston, variations in said servo pressure arising from relative displacement between said piston and said spool urging said piston in directions to reduce the relative displacement, a chamber axially aligned with said piston, a plunger slidable within said chamber and coupled to said spool, means for supplying a second pressure signal to said chamber, and element slidable within said chamber and engageable with an abutment on said plunger, means biasing said element against said abutment to urge said plunger against said second pressure signal, and an extension of said plunger, in the region of said chamber, having bores therein which are in constant communication with said chamber so as to be subjected at all times to pressure within said chamber.
 2. The arrangement according to claim 1, wherein said chamber is connected to a low pressure drain via a restrictor
 3. The arrangement according to claim 1, wherein said plunger is provided with a nut assembly thereon forming said abutment, said element is mounted with a clearance on said plunger, and said biasing means comprises a spring mounted in said chamber and disposed to urge said element into engagement with said nut assembly.
 4. The arrangement according to claim 1, wherein an adjustable stop is provided for limiting axial movement of said plunger by said biasing means.
 5. The arrangement according to claim 4, such that abutment of said plunger against said stop, in use, corresponds to a position in which the machine is at zero stroke.
 6. The arrangement according to claim 5, such that abutment of said plunger against said stop, in use, corresponds to a position in which the machine is at the maximum stroke.
 7. A hydraulic pump and motor system incorporating an actuator arrangement as claimed in claim 1, wherein the actuator arrangement is connected with a stroke control for the pump, the first Pressure signal is derived from that side of the pump which, in use, is at a higher pressure and the second pressure signal is derived from a control pressure.
 8. A hydraulic pump and motor system incorporating an actuator arrangement as claimed in claim 1, wherein the actuator arrangement is connected to a stroke control for the motor, the first pressure signal being derived from that side of the motor which, in use, is at a higher pressure and the second pressure signal is derived from a control pressure.
 9. A hydraulic pump and motor system incorporating an actuator arrangement as claimed in claim 1, wherein the arrangement is connected to a stroke control for the motor, the first pressure signal is derived from that side of the pump which, in use, is at a higher pressure and the second pressure signal being derived from the pressure at an outlet of the motor. 